This application claims the benefit of Ukrainian Application No. 99127035, filed Dec. 23, 1999 in the Ukrainian Patent Office, and Korean Patent Application No. 00-55753, filed Sep. 22, 2000, in the Korean Patent Office, the disclosures of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a black matrix and a preparing method thereof, and more particularly, to a black matrix which is a black coating layer which surrounds the pixels of a display device, a preparing method thereof, and a display device employing the black matrix.
2. Description of the Related Art
A black matrix, which is a light-absorbing black coating layer for absorbing external light and dispersed emission from neighboring patterns, is formed between phosphor layers of a color cathode ray tube (CRT) or other kinds of display devices. The black matrix features the outer appearance of colored pixels of an overall display device and improves the contrast of a displayed color image.
The black matrix of a color CRT is generally manufactured in the following manner. That is, a graphite dispersive solution is coated and then a photolithography process is performed to form a pattern. Alternatively, a metal oxide (MO) (here, M is either Cr or Ni) and a metal are vacuum-deposited to form a light-absorbing coating layer and patterned by a photolithography process. In addition, a method of forming a black matrix by depositing film-like layers on the inner surface of a display panel using a reactive sputtering method is disclosed in U.S. Pat. No. 5,976,639.
According to this patented invention, the film-like layers include a transition layer and a metal layer. Here, the transition layer is formed such that the concentration of a metal such as chromium (Cr), tungsten (W), tantalum (Ta), titanium (Ti), iron (Fe), nickel (Ni), or molybdenum (Mo) gradually increases in an incident direction of light at a proportion of 0.5 to 20% per 100 xc3x85 in film thickness. Also, chromium (Cr) is mainly used as the metal component and the material for forming the metal layer. The thickness of the metal layer must be in the range of 1,000 to 1,400 xc3x85 so as to shield a back light beam. Also, the content of the metal contained in the metal layer must be controlled to be in the range of 50 to 100% of the concentrations of all metals contained in the film-like layers. In some cases, the transition layer may further include elements of oxygen, nitrogen or carbon.
As described above, the film-like layers mainly employ environmental contaminants such as chromium, and deposition thereof must be performed under oxygen atmosphere. Also, during formation of the transition layer and the metal layer forming the film-like layers, the compositions and thicknesses of the respective layers must be strictly controlled. Thus, the manufacture of the film-like layers is quite complicated process.
Alternatively, the black matrix may be formed using a vacuum thermal deposition method, as disclosed by the inventors of the present invention, E. Shepeliavyi P., Z. Indutnyy I., and V. Michailovskaya E. in Russian Federation Patent No. 2052864 and Optical Engineering Bulletin No. 2(6), 1995, pp.16-17. According to this method, a black coating layer is formed by depositing a mixture consisting of 70 to 90 wt % of Cr and 10 to 30 wt % of SiO on the inner surface of the color CRT. As the deposition temperature gradually increases, SiO, which is a dielectric material, is first deposited, and both Cr and SiO materials are simultaneously deposited at a higher deposition temperature, and Cr, which is a metal element, is finally deposited at the highest deposition temperature. The mixture ratio of SiO to Cr in the resultant coating layer is continuously changed throughout the coating layer from a pure dielectric material layer on one surface of the coating layer to a pure metal material layer on the other surface thereof. As described above, a desired black matrix pattern is formed such that a black coating layer is first formed and then the black matrix pattern is completed by a photolithography process. Alternatively, a photoresist pattern is first formed by coating photoresist and exposing and developing the same, a black coating layer is then formed on the photoresist pattern, and the photoresist pattern and an undesired black matrix coating layer are finally removed by an etching process, thereby forming a desired black matrix pattern.
The thus-formed black matrix has several advantages in that it is excellent in view of a low coefficient of light diffusion reflection, thermal stability, physical and chemical characteristics compared with the black matrix formed using a colloid-graphite dispersive solution, and does not produce gas pollution when heated. However, the thus-formed black matrix has the following disadvantages. First, the above-described method is undesirable in view of environmental protection because chromium, which is a toxic substance, is employed to this method. Second, the non-homogenous coating layer, deposited on an unheated substrate, is internally stressed and unstable in mechanical characteristics. Thus, in order to obtain an unstressed and stable coating layer, it is necessary to continuously vary the temperature of the substrate while a deposition process is performed, which is quite complex process compared with general vacuum deposition equipment.
To solve the above problems, it is an object of the present invention to provide a black matrix which has excellent adhesion to a substrate without an annealing process, by using a mixture of a nontoxic metal other than chromium and a dielectric material, which is excellent in a mechanical characteristic due to the absence of internal stress and which is excellent in accomplishing an external light absorbing effect.
It is another object of the present invention to provide a method of preparing the black matrix using general vacuum deposition equipment.
It is still another object of the present invention to provide a display device having improved luminance and contrast characteristics by employing the black matrix.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the first and other objects of the present invention, there is provided a black matrix which is a black coating layer surrounding pixels of a display device, the black matrix including SiO which is a dielectric material and at least one metal selected from the group consisting of iron (Fe), cobalt (Co), vanadium (V) and titanium (Ti).
Preferably, the content of SiO gradually decreases and the content of metal is gradually increases, along an incident direction of external light.
The mixture ratio of the dielectric material to the metal is preferably 20:80xcx9c50:50 by weight.
The second and other objects of the present invention are achieved by a method of preparing a black matrix including injecting into a deposition boat a mixture consisting of 20 to 50 wt % of SiO which is a dielectric material and 50 to 80 wt % of at least one metal selected from the group consisting of Fe, Co, V and Ti, the mixture components having different melting points, mounting a panel of a display device on a vacuum deposition device and depositing SiO and metal while varying the temperature of the deposition boat, and patterning the resultant structure by a photolithography process.
In the step of depositing SiO and metal, while the temperature of the deposition boat gradually increases, SiO is first deposited, and both SiO and metal are simultaneously deposited at a higher temperature and metal is deposited at the highest temperature. Thus, SiO is distributed such that the content thereof gradually decreases along an incident direction of external light, and the metal is distributed such that the content thereof gradually increases along the incident direction of external light.
The third and other objects of the present invention are achieved by providing a display device employing the black matrix. In a preferred embodiment of the present invention, the display device includes a color cathode ray tube or a liquid crystal display device.